Technical Field
The present disclosure relates to an interface for expanding the dynamic interval of an input signal, in particular of an audio signal of an acoustic transducer having two detection structures, and to the related method.
Description of the Related Art
Acoustic transducers are known, for example MEMS (MicroElectroMechanical System) microphones, comprising a micromechanical sensitive structure, configured to transduce acoustic pressure waves into an electrical quantity (for example, a capacitive variation), and a reading electronics, configured to execute appropriate processing operations (including amplification and filtering) of the electrical quantity for supplying an electrical output signal, whether analog (for example, a voltage) or digital (for example, a PDM—Pulse Density Modulation—signal).
The electrical signal, possibly processed further by an electronic interface, is then made available for an external electronic system, for example a controller of an electronic apparatus incorporating the acoustic transducer.
The micromechanical sensitive structure in general comprises a mobile electrode, implemented as a diaphragm or membrane, facing a fixed electrode to form the plates of a variable capacitance sensing capacitor. The mobile electrode is generally anchored, through a perimetral portion, to a substrate, while a central portion thereof is free to move or bend in response to the pressure exerted by incident acoustic pressure waves and thus to modify the capacitance of the sensing capacitor. This capacitance variation affects the electrical signal generated by the sensitive structure (typically the voltage across the capacitor).
In general, the electrical performance of the acoustic transducer, and in particular its sensitivity, depends upon the mechanical characteristics of the sensitive detection structure, and moreover upon the configuration of the associated, front and rear, acoustic chambers, i.e., the chambers facing a respective, front or rear, face of the diaphragm and traversed in use by the pressure waves incident on the diaphragm and departing therefrom. These different characteristics are thus exploited in order to obtain a wide dynamic interval.
In fact, in numerous applications it is important to detect acoustic pressure waves with a wide dynamic interval, i.e., signals having a low SPL (Sound Pressure Level), a high sensitivity, and a high SNR (Signal-to-Noise Ratio) and signals having a high SPL, a lower sensitivity, and a reduced SNR.
Consequently, in the detection of acoustic pressure waves, it is important to reach an optimal compromise between wide dynamic interval, high sensitivity, and high signal-to-noise ratio.
U.S. Pat. No. 6,271,780 describes a solution for increasing the dynamic interval in an acoustic system, comprising an ADC (analog-to-digital converter), configured to receive an analog sensing signal from an acoustic transducer. This solution envisages subjecting the analog input signal, in parallel, to two signal processing paths, having a first, analog, portion and a second, digital, portion, and each having a respective amplification and gain factor for adapting to signals with low and high sound pressure level, respectively. The two digital signals at the output of the two processing paths are combined for supplying a resulting output signal. Prior to combination, the two signals have be subjected to an equalization, to take into account differences of gain, offset, and phase generated by the previous operations of processing of the signal, in part of an analog type, and thus prevent any distortion of the resulting output signal.
The above solution is not free from problems, linked principally to the complexity of the processing chain, to a non-negligible sensitivity to noise and oscillations of the input signal, to a low configurability, and to a non-optimal signal-to-noise ratio.
Another solution is described in US Patent Publication Number 2014/0133677 in the name of the present applicant.
In general, the present disclosure is directed to an improvement over the known solutions in order to extend the dynamic interval in the detection of signals, such as acoustic pressure waves, at the same time reducing the onset of artefacts during switching between channels.